The electrostatic levitation furnace, after charging a sample inputted between main electrodes utilizing electrode contact, ultraviolet ray irradiation, or heating, puts the sample to a levitation state by an electrostatic field generated between the main electrodes, while maintaining the sample at a predetermined position by controlling a potential between the main electrodes or auxiliary electrodes, and irradiates laser light on the sample to heat and melt the same. By cooling and solidifying the sample thus heated and melted, crystals can be produced in a state that external interference has been excluded.
It is necessary to control levitation of a sample so as to prevent swinging of the sample or suppress the same as much as possible through generating crystal in the electrostatic levitation furnace in order to improve quality, and it is important to recognize a position of the sample accurately in order to perform control on such sample levitation.
Conventionally, as a means of recognizing a position of a sample, for example, there are a position recognizing method which uses laser light as background light and detects the highest luminescent spot or a statistical center of the luminescent spots except for a portion shielded by a sample formed in an almost spherical shape using a photo sensor to output position information, and a position recognizing method which uses laser light as background light like the above approach and processes an image of a sample photographed by a CCD camera to calculate a position of the center of gravity and output the same as position information.
In the conventional art, however, since a position of the center of gravity of the sample is not calculated in the former position recognizing method, the method does not excel at accuracy in position recognition of a sample except a spherical one. As a result, there is such a problem that it becomes considerably difficult or impossible to perform levitation control on a simple.
On the other hand, in the latter position recognizing method, the position of the center of gravity of a sample is calculated, but since it takes much time to perform image processing and a sampling speed required for levitation control can not be secured, there is such a problem that the latter method can be used only rarely.
Further, in case that a halogen lamp is used for the background light, when the sample becomes incandescent due to a high temperature, it is impossible to obtain a contrast of a sample against a background, so that laser light is adopted as the background light in the latter position recognizing method (see FIG. 3). However, for convenience of using a CCD camera, there is a problem about interference of laser light due to a camera lens.
Moreover, in the position recognizing methods, since such a constitution is employed that an instant at which a sample has melted is determined by measuring a temperature of the sample using a radiation thermometer, it is always required to correct an emissivity. There is such a problem that it is difficult to specify a melting time correctly. It is the conventional subject to solve these problems.